The commercial and governmental space sector faces high costs in placing and maintaining communication and other satellites in orbit around the earth. A satellite's life is typically governed by the amount of on-board propellant carried by the satellite. Even when onboard electronics are still functional, once the fuel runs out, a satellite typically loses its usefulness. As demand for satellite connectivity has increased over time, so has typical satellite size. A substantial initial investment is required to launch a large geostationary communication satellite. The initial investment for a satellite service provider includes not only the cost of the satellite itself, but also the cost of the launch vehicle required to inject the satellite from earth into an injection orbit.
A satellite typically includes its own propulsion system, which allows the satellite to transition itself from an injection orbit to a final geosynchronous orbit and to maintain its orbital position for up to 15 years. Propulsion system technology has also matured throughout the years and allows the satellite to make use of not only chemical systems but also electrical propulsion systems that have a much higher efficiency. This increased efficiency saves fuel, which in turn allows placement of larger and/or heavier satellites in orbit.
A satellite in a geostationary orbit around the earth experiences gravitational and solar forces, which tend to move the satellite away from its desired geostationary position. The satellite relies on its propulsion system to take corrective measures to compensate for the displacements caused by the gravitational or solar forces. The propulsion maneuvers required to maintain the geostationary position of the satellite are sometimes referred to as station keeping. When a satellite depletes is entire on-board fuel, it can no longer use its propulsion system to maintain its geostationary position and may have to be replaced.
In some cases, the satellite launch vehicle may underperform, injecting the satellite into an incorrect orbit. The satellite may then have to expend its on-board fuel to transition itself from the incorrect orbit to its correct orbit. Thus, some of the fuel intended for station keeping may have to be used for initial orbit correction, which in turn may result in a shorter operational life of the satellite, providing less revenue to the satellite service provider. In other cases, a satellite may be required to change its orbital position and/or orientation for various commercial or operational reasons. These changes may also require the satellite to expend its on-board fuel, resulting in a shorter operational life.
Because of the high cost associated with replacing a satellite in space, there is a need for technology that may help to extend the life of a satellite already in orbit.